The field of the disclosure is related to superconducting circuits. More particularly, the disclosure relates to systems and methods for controlling superconducting quantum circuits using single flux quantum (“SFQ”) logic.
In the field of quantum computation, the performance of quantum bits (“qubits”) has advanced rapidly in recent years, with preliminary multi-qubit implementations leading toward surface code architectures. In contrast to classical computational methods that rely on binary data stored in the form of definite on/off states, or bits, methods in quantum computation take advantage of the quantum mechanical nature of quantum systems. Specifically, quantum systems are described using a probabilistic approach, whereby a system includes quantized energy levels whose state may be represented using a superposition of multiple quantum-mechanical states.
Among several implementations currently being pursued, superconductor-based circuits present good candidates for the construction of qubits given the low dissipation inherent to superconducting materials, which in principle can produce coherence times necessary for performing useful quantum computations. In addition, because complex superconducting circuits can be micro-fabricated using conventional integrated-circuit processing techniques, scaling to a large number of qubits is relatively straightforward. In particular, superconducting circuits that include Josephson tunnel junctions, generally composed of two superconducting electrodes separated by a thin insulator, may be utilized for scalable quantum information processing in the solid state. Such Josephson junction-based superconducting circuits are advantageous on account of their strongly nonlinear behavior, which allows a breaking of degeneracy for the transition frequencies, and thus restricting system dynamics to specific quantum states.
Presently, gate and measurement fidelities are within reach of the threshold for fault-tolerant quantum computing based on topological surface codes, and hence there is interest in scaling quantum computing devices that include a few qubits to much larger, multi-qubit circuitry. However, a superconducting quantum computer that will outperform the best available classical machines may necessitate thousands if not millions of physical qubits, and hence the wiring architecture and control of a such large-scale quantum processor presents a formidable technical challenge.
Present systems for measurement and control of superconducting quantum circuits typically include low-temperature systems, such as dilution refrigeration units. Such systems are configured with microwave frequency generators and single-sideband mixing hardware that generate and transmit microwave electromagnetic signals to multiple superconducting circuits for purposes of measurement and control of the state of each qubit. However, such systems are limited in terms of wiring availability, as well as thermal and noise coupling to room temperature electronics. Hence, in applications involving cryogenic temperatures it is highly desirable to integrate as much of the control and measurement circuitry for a multi-qubit system as possible into in order to reduce wiring heat load, latency, power consumption, and the overall system footprint.
Given the above, there a need for systems and methods yielding scalable quantum computation that includes the ability to perform rapid high-fidelity control and measurement of both single qubits and multi-qubit parity, while controlling the resources utilized.